The present invention relates to controlled release coated agricultural products, particularly agricultural chemicals and seeds, and to the process of making the same.
It is known to coat agricultural chemicals ("agrichemicals"), such a fertilizers, soil conditioners, fungicides, insecticides, herbicides, nematocides, plant hormones, insect repellents, and the like, in order to control their release over varying periods of time after they have been applied. The purpose is to permit controlled release thereof over an extended period of time and thereby ensure that the beneficial effects are maximized, or to delay the release thereof until such time as it is desired that the beneficial effects be used.
The coatings that have been used for these have varied, some of them being released by environmental dissolution factors, such as the air, oxygen, or water, and some by microbial degradation, and some by a combination of all. Toward this end, these have include a variety of polymers and other materials such as waxes and the like. To date, however, none of such coatings has been satisfactory for a variety of reasons. Thus, for example, it has been known to coat agrichemicals, such as urea, with sulfur in which the semi-crystalline sulfur coats the urea, provides small channels for the entrance of water, and the subsequent extraction of urea. Polymer or wax coatings are applied to seal the small channel or cracks and the sulfur layer to obtain a longer term or a delayed release. The operative mechanism for release is diffusion control through the microcrack sealed polymer. However, it is difficult to control the rate of release due to the difficulty in controlling the number and sizing of the microcracks and the amount of polymer or wax as needed to seal the same in order to get the desired release schedule. In agricultural usage, it is important that the release be predictable in order that the agrichemical be released at the proper time in the growth cycle of the particular crop to which it has been applied. If, for example, a pesticide is to be applied, but it is not released until after the time at which the attacking pest is due to act on the plant it, of course, becomes essentially a worthless product.
With respect to seeds, certain of them, such as corn, are especially susceptible to premature swelling by water-laden soils, which can prevent their proper germination. It has long been desired to protect such seeds from such excess water with a hydrophobic coating which would be capable of biodegrading at a known rate. This would enable the seed to be sown at a desirable time or even under adverse conditions, and through bacterial erosion of the coating have the seed available for germination under less adverse conditions. Such coatings previously used, however, have a number of drawbacks, some of which require the use of solvents, which are often deleterious to the seed. In addition, as previously noted, certain of them, such as sulfur coatings, tend to have microcracks and, as such, difficult to properly coat them to get the desired release rates.
There are also coating procedures which utilize materials which are costly and make them uneconomic and often the coating materials themselves are deleterious to the environment. This is particularly true with certain of the polymers which utilize formaldehyde, which can adversely affect the soil.